Shaping DNA Damage Response Networks Via Histone H2a Variants

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PROJECT SUMMARY Genome organization is driven by chromatin, the fundamental unit being the nucleosome that is made up of histone proteins. In addition to canonical histones, histone variants exist that diversify chromatin and play specialized roles in genome maintenance. Although best studied in transcription, histone H2A variants in particular are emerging as critical participants in DNA damage responses including DNA repair that protect cells from the constant threat of endogenous DNA damage and mutations, which are known to be drivers of human diseases including cancer. Based on our studies, macroH2A1.2 plays vital functions in DNA repair and DNA damage associated transcriptional regulation. Here, we will employ innovative biochemical and cell-based systems to identify mechanistically how macroH2A histone variant, in collaboration with PARP1 and the histone demethylase KDM5A, orchestrate DNA damage response functions. Specifically, we will determine how macroH2A and KDM5A are involved in radiation and PARP inhibitor (PARPi) responses. We hypothesize that PARPi can interfere with KDM5A function and that effector proteins promote the function of these factors at breaks, including transcription regulation and HR repair. We will identify macroH2A functions in DNA repair and therapeutic responses using cancer and non-transformed cell lines. Using cell complementation, we will define the specific interactions, domains and modifications involved in these pathways and responses. Although macroH2A, KDM5A and other macroH2A effector proteins are known to be involved in cancer, these studies will identify their genome integrity functions and importance for DNA damage responses involving radiation and PARPi. Our long-term goals are to define mechanistically how chromatin and its associated factors contribute to genome integrity and how deficiencies in these pathways can be targeted in cancer. This proposed work contributes to these goals through a combination of genetic, biochemical and cellular approaches in human cells to identify and define macroH2A pathways that promote genome integrity, including through DNA repair and transcriptional responses. These studies will deliver new mechanistic insights into how this pathways protects the genome and determine if dysregulation of this pathway in cancer can provide opportunities for therapeutic interventions.